Automatic control for anti-icer apparatus for aircraft



Sept. 2 6, 1944.

G. v. HOLLOMAN ETAL 2,358,804

AUTOMATIC CONTROL FOR ANTI- ICER APPARATUS FOR AIRCRAFT 2 Sheets-Sheet 1,

Filed Feb. 10, 1940 650265 1/ I7'OLLOM4/V G. v. HOLLOMAN ETAL 2,358,804

AUTOMATIC CONTROL FOR ANTI-ICER APPARATUS FOR AIRCRAFT Sept. 26, 1944. 7

Filed Feb. 10, 1940 2 Sheets-Sheet 2 7 TOQ VEY.

Patented Sept; 26, 1944 AUTOMATIC comer. roa Ami-roan mm'rus roa AIRCRAFT George V. l lolloman and William E. Huflman,

Dayton, Ohio Appllcation'February 1o,194o,"ser|ai m.s1s,zes

9 Claims. (01. 244-134) '(Granted under the note! March a, less, as amended April 30,1928; 370 o. G. 751) The invention described herein maybe manufactured and used by-or for-the Government for governmental purposes, without the payment to us of any royalty thereon.

This invention relates to'improvements in aircraft and more especially has to do with means for automatically controlling the operation of ice-prevention or ice-eliminating apparatus for the wing and other surfaces of aircraft.

An object of the invention is to provide a control of an efllcientreliablenature that will act automatically to bring the ice-prevention or ice-' eliminating apparatus into play at the proper time when ice-forming conditions occur, and that will so regulate the operation of said appa-v ratus as to prevent the formation or accumulationof ice on'the exposed surfaces of the aircraft, and will stop the operation of said apparatus when ice-forming conditions cease.

Another object of'the. invention is to provide.-- in conjunction with an automatic control of the character referred to, signalling means that will warn the pilot when ice-forming conditions pre -vail and also indicate that 'the ice-prevention or ice-eliminating apparatus is in operation.

The invention, with other objects and advanfor controlling various'kinds of ice-prevention, or ice-eliminating apparatus. In the particular exempliflcations of the invention illustrated in the drawings, the'control means-is shown in connection with anti-leer apparatus of the type compr sing inflatable memberstassociated with thewingand other surfaces of an airplane, and

"means for suppl ing fluid pressure to the inflatable members. i Referring to the embodiment of the invention illustrated in Fig. 1. oi the drawings,v the particular construction of 'anti-icer apparatusshown by way of example. is awed-known form of such. apparatus and is therefor indicated only in a general way;

The expansible members l,- 2, ands oi the anti-leer apparatus-are connectedtoa rotary distributor, valve 6, through suitable-pipe-com nections as shown. A rotary air pump 5 suptages thereof, and the particular construction.

combinations, and arrangements of parts com prising .the same, will be understood from the hereinafter-contained detailed description when considered in connection with the accompanying drawings forming part thereof and illustrating several embodiments of the invention.

In the drawings: Fig. lis a diagrammatic view of a control vention.

plies fluid pressure. to said members through an exhaust conduit 8 connected to the rotary valve. 1 is an exhaust port to thevalve ii, and B is an intake port to the pump 5. The speed of the distributor valve is regulated. by means or; a reduction gear drive 8 between the pump and the valve. The distributorvalve acts to periodically connect the expansible members or overshoes I, 2, and 3 with the pumpt when the latter is operated.

Referring to a detailed description oi the automatic control, It designates an electric motor-for-driving' the-pump 5 of the anti-icervapparatus, the motor being connected at one terminal by a conductor wire H with one side of fconstructed "in accordance with the present in- I Fig. 2is diagrammatic showing of a modified construction. J p

Fig. 3 is a diagrammatic view of a modified form o f-ice detector and diaphragmv unit.

Fig. 4 is a perspective view of a cam makeand-break switch "which may be used in lieu of a rotary switch.

While several preferred embodiments'of the invention are illustrated in the drawings, it. will of course be understood that minor changes and modifications may be made in the particular constructions shown, and the invention may be embodiedin other !or'ms,.aswill appeal to. those skilled'in the art, falling. within the scope of the appended claims, without departing from the spirit of the invention.

The control-,means provided in' accordance .withvthe-present inventionisJsusOeDtible of use a storage battery I! or other suitable source of electrical energy. nd havingi'at the other ter minal a conductor I8 .connecttd with circuitcontrolling devices that are responsive toatmosj pheric ice-forming conditions. I The circuit-controlling devices-include a ven- I tori H or similar device appropriately mounted onthe aircraft to face toward thelfront thereof at a point where ice is most likely to form. The

- venturi is provided with an electric heater coil l5. As-lllustrated, a diaphragm i6 is connected to the venturi by a pipe I! to be responsiveto change of pressure in the venturi due to col-' pipe n; and when ice collects'in the venturi lection of ice therein, so. that when the venturi is free of ice thediaphragm is held collapsedby the suction or-iow pressurecreated in the",

and the latter-no longer'acts to create auction in said pipe, the diaphragm expands. The pipe '11, or diaphragm I6, is provided with vent vmeam, being. as illustrated, in the form or an its free end contacts20 and 2|.

. the diaphragm is collapsed.

aperture l1a in the pipe, the aperture being sufficiently small to break the vacuum sealed in the diaphragm when the venturi ices up," thus enabling the diaphragm to expand, but not so large as to render inefiective the suction efiect of the venturi. The diaphragm as shown is provided with a spring l8 to force the same open when it is relieved of the low interior pressure conditions. Obviously, a metallic bellows or Sylphon could be used in lieu of the bellows, in which case the spring would be unnecessary.

The movable wall l6 of the diaphragm is provided with a contact carrying arm l9 having at The contact 20 is adapted tov engage a stationary contact 22 when the diaphragm expands. Contact 2| is adapted to engage a stationary contact 23' when On the movable wall l6 of the diaphragm is also a contact 24. This contact engages a stationary contact 25 when the diaphragm is expanded. To the stationary contact 25 is connected the conductor wire l3 of the motor l6.

The circuit-controlling means also includes a pair of rotary switches 26, 21 and an electric motor 28 for actuating the same. Each of-the switches comprises a suitably supported stationary base member of insulating material provided on one face with a plurality of concentrically ar ranged spaced contacts and arotary contact armto cooperate therewith, secured at one end to a shaft that is supported for rotation centrally of the base of the switch and the plurality of contacts thereon. The base. 26' of the switch .26 is provided with an inner annular contact 29 and outer contact segments 30, 3|, 32, and 33. 34 designates the rotary contact arm. The base member 21' of the switch 21 has an inner ring contact 35 and outer contact segments 36 and 31. The rotary contact arm. of this switch is designated 38. The rotary contact arms 34 and 38 of the switches. are each connected to the motor 26 by a reduction gear so that they will be rotated clockwise in unison at a very slow rate of speedfor example, around one-sixth of a revolution per minute. In the particular construction shown, the rotary contact arms 34 and 38 of both of the switches are secured to a single shaft 39, said shaft having end portions extending through central openings the base members of the switches, and the shaft is connected by a. suitable reduction gear 40 to the motor 28. The motor 26 has a conductor 4|, connected with the' contact arm Is on the movable wall l6 of the diaphragm, and a conductor 42 connected with the conductor wire ll. The contact segment 31 of the switch 2115 connected to the contact 24 on the movable wall l6 of the diaphragm by a conductor 43. The contact segment 36 of said switch is connected by a conductor 44 with the conductor l3, and this contact segment is also connected by a conductor 45 to the inner annular contact 29 of the switch 26. The annular contact 29 is connected by a conductor 46, throughthe automatic position of a switch 41, more completely hereinafter described, and the conductor 56 to by conductors 49 and 56. The electric heater l5 of 'the venturi has a conductor 5| connected to one'slde of the storage battery l2 through conductor II, and a conductor 52 connected to the contact segment 33 of the switch 26.

The switch 41 interposed in the conductor 46 is a manual control switch, the same comprising a switch member 53 pivotally connected at one end to a base 41 that is provided with contacts 54-and 55, denoting the automatic (auto) position of operation of the control circuit and the on position, respectively. The conductor 46 is connected to the automatic contact 54 on the base. The switch member 53 of said switch is always in contact with battery |2 through conductor 56. The on" contact 55 of the switch is connected by a conductor wire 51 with the motor In. As will be understood, this switchprovides for cutting out the automatic control and operating the motor l0 and the anti-icer apparatus independently thereof, and for cutting out the system entirely.

58 designates an electric lamp or other suitable form of signalling device, The lamp, which is mounted on or near the instrument board of the aircraft, has a conductor 59 connected to the conductor wire 51, which is in contact with conductor wire |3 at the motor I6, and a'concluctor 6|] connected tothe other conductor wire ll of said motor.

Operation As will be understood, the venturi, when its" heater is not in operation, isimuch more suscep tible to ice formation than the wing and other surfaces of aircraft. At the start of the cycle, the rotary contact arms 34 and 38 are in the positions shown in Fig. 1 of the drawings, rotary contact arm 34 of switch 26 engaging the contact segment 3| and rotar contact'arm 38 of switch 21 engaging contact segment 31.

When ice forms in the venturi l4, suction through pipe [1 on diaphragm l6 ceases, the vacuum in the diaphragm I6 is relieved through the vent- No, the diaphragm expands, and contacts 2| and 24 on the movable wall l6 of the diaphragm, respectively, engage the stationary contacts 22 and 25, A circuit is completed from storage battery |2 through conductor 56, switch member 53, conductor 46, innerannular contact 29 of switch 26, conductor 45, inner ring. contact 35 of switch 21, rotary contact arm 36, conductor 43, and conductor l3 to motor H1 and back to the battery through conductor H, the motor Ill being set in operation to operate the anti-icer annular contact 29 of switch 26, rotary contact arm 34, conductor 49, conductor wire 4| to motor 28 and through conductors 42 and II back to ithe battery, starting the motor '28, and the rotary contact arms 34, 38 are rotated clockwise at slow speed. When rotary contact arm 34 of switch 26 reaches contact segments 32 and 33, the motor 28 stops, the circuit of the motor being opened at the contact segment 3| of switch '26. At this time a circuit to the electric heater I5 of the venturi is completed from storage battery I2 through conductor 56, switch member 53, conductor 46, annular contact 29 of switch 26, rotary contact arm 34, contact segment 33, conductor 52, electric heater l5, and conductor 5|. The

motor In continues to operate, since the rotary contact arm 38 of switch 21 has now established a circuit to the motor through conductors l3 and 1' 44, across the contact segments 36 and "35,

aasaaoe through conductor 45, annular contact 2! of switch 28 and conductor ll to battery I2, thereby "shorting" that part of the previous circuit through contacts 28 and 2!.

The system may now be said to be in the secondary stage of its cycle-that is, ice has accu mulated 'inthe "venturi, the diaphragm has expanded, rotary contact arm 33 of switch Il'has .moved to segment all, rotary'contact arm 34 of --circuit is completed from the battery I2 through switch member 53, conductor st, annular contact :s of the switch 26, rotary contact arm ,contact segment 32, conductor 50,, conductor wire ll to motor 28, and through conductors 42 and ii. back to the battery, the motor 28 being set in operation to turn the rotary contact arms 34 and 39 of the switches. Rotary contact arm 35 of switch 28 is moved from contact segments 32, 33 to segment 30 and continues to rotate,'since the circuit to motor 28 is now completedthrough conductor as in lieu of conductor 50. Likewise, rotary contact arm 38 of switch 21 rotates in contact with inner ring contact 35 and contact segtut, means for warning'the pilot when ice-forming'conditions occur, and also for indicating that the anti-icer apparatus is in operation. In" the modifled'iorm of control illustrated in 2 olthe drawings, there is only one motoractuated rotary switch, and, as shown, this is actuated by the same motor that operates the anti-icer apparatus. However, it it is desired, a separate motor may be used to actuate the switch in a manner similar to that peri'ormed by-the motor in Fig-"1." The anti-icer apparatus shown in this view is the same as that illustrated in 1"lg.-1. 65 designates the rotary air pump-for supplying pressure to the expansible members or overshoes 68, 81, and 68; "is the rotary distributor valve; and It is the reductiondrive gear connection between the pump andthe valve.

The electric motor 1 I for driving the pump 85, is connected by a'conductor wire 12 to one side of the storage battery 18 and has a conductor wire 16 connected with the circuit controlling devices hereinafter described. The circuit-controlling devices, as in the formoi control illustrated in Fig. 1, include a venturi 15 or similar device, provided with an-electric heater coil 16, and 9. diaphragm 11, provided with a spring 18 and connected to the venturi by a pipe 19, having a vent aperture isa, so that when the venturi is free of ice, the diaphragm is held collapsed by; the suction created in the pipe l9, and when ice collects in the venturi and it stops producing suction in ment 36. The system is now in the third stage of its cycle. The ice having melted, there is free passage of air through the venturi; the motor is is running, turning the rotary contact arms 38. 88; and the motor it is running, operating the anti-icer apparatus. If no ice forms during the time it takes rotary contact arm 84 of switch fitl to travel clockwise from contact segments 33, stand 3@ to contact segment 3! operation'of the system will stop, since with the diaphragm collapsed, contacts 2| and Hon the diaphragm are disengaged irom stationary contacts 22, 25, and the circuits to contact segment 3! of switch it and to contact segment 3'! of switch 2! areopen.

In the event ice does form while rotary contact'arm as of switch as is travelling irom contact segments 82,33, and .35 to contact segment 35, the cycle will be repeated and will continue until ice-ioriningconditions no longer prevail.

It will he noted" that, by the particular combination and arrangement of parts hereinbefore' set forth, a control is provided that will act automatically in an eficient, satisfactory manner to b into operation the anti-icer apparatus at the proper time when ice-forming conditions occur," that will keep the anti icer apparatus in operation for the proper period, will so regulate the operation of the same as to prevent the accumunot needed. it will also be observed that the control hereinbefore described also provides, in connection with its control of the anti-icer apparathe pipe is, the diaphragm expands.

0n the movable wall ll oi the diaphragm is a contact to, which is adapted to engage a stationary contact ti when the diaphragm expands. 4 The motor-actuated switch of this form oi the a control comprises a base 82 of insulating material, provided on one face thereot with ,an inner ringcontact 83; outer contact segments 04, 85, and; and a rotary contact arm 81. The rotar-y contact arm 81 is secured at one end to a shaft 88, suitably supported for rotation-centrally of the base 82 and'the contacts thereon, said shaft extending through a central opening in the base. The shaft is connected by a -reduction gear as to the shaft of the motor 7! to be driven clockwise at very low speed-for instance, one sixth of a revolution per minute or there'aboutsthe s as the rotary contact arms of the switches in the construction illustrated in Fig. l.

The stationary contact ti is connected by a conductor wire as with the contact so cut 84 of the rotary switch, and the contact ll on the movable ,wall it otthe diaphragm is connected by a conductor at to the segmental contact 85 and also connected by conductor 82 to the condoctor is of the motor. The inner ring contact 83 is connected by a conductor 93 through the automatic position of a switch 94 to one side of w The electric heater it has a conductor 99: that is connected to the outermost segment 86 of the,

switch and connects to one side of the battery it by means-oi conductor l2.

7 its is the signalling device, having a conductor operated in any' suitable way.

heating coil vfor the straight tube portion I95. -the heating coil having conductors Ill and H4.

The movable wall II5 of the diaphragm has an arm I I6 carrying a contact II1 which is adapted to engage a statlonarycontact III when the diaphragm is collapsed. -II 9 designates a con- "I connected with the conductor 12 of the motor and a conductor I02 connected with the conductor wire 14 of the motor.

This modified form of control system operates as follows: At the beginning of the cycle the rotary contact arm 51 of the switch is in the position shown in the drawings, in engagement with the contact segment 94. When ice forms in the venturi, suction through pipe 19 on diaphragm 11 ceases, the diaphragm expands .and

contact 80 on the movable wall 11 of the diaphragm is moved into engagement with the stationary contact and a circuit is established through conductor 90, contact segment 94 of the 1 switch,rotary contact arm 91, inner ring segment 83, conductor 93, switch member 91, con-v ductor 99, battery 13, conductor 12, motor 1I, conductor 14, conductor 92, and conductor wire erate the anti-feet apparatus. With the completion of the motor circuit,"a circuit is.established to the signal lamp I00, through the con-' ductors IN and I02; and the contact arm 91 of the switch is now turned veryslowly by the motor. When the contact arm'l1 reaches contact segment 95, a circuit to the heating coil 15 of the venturi is completed from battery 13 through conductor 12, conductor 99,,contact segment 99, rotary contact arm 51, inner ring confunction long .enough to melt the ice in the venturi.

for the motoris. completed from the battery through conductor 12, conductor 14-, conductor 92, conductor 9I-, contact segment 95, rotary conswitch member 91, and conductor 99 back to the battery. As will be understood. if ice does not again collect in the venturi during the time it takes rotary contact arm 81.to travel clockwise from the contact segment 95 to contact segment 94, the motor will stop, the'motor circuit being I opened by the collapsingoi' the diaphragm. If ice again forms in the venturi during the time it'takes the rotary contact arm 91 to travel from the contact segment .95 to contact segment 94,

the system willcontinue in operation. v Y In Fig. 3 of the drawings is shown a modified form'of ice detector and control tube. consist of a plainstraight tube portion I95 hav-' ing a slightly flarin forward end and a .c

rearward extension I09 having two branches-s I01 and I09. A continuously-driven rotary sue tionpump I09 is connected to the tube Illby meansof branch I05, and diaphragm, IIO'is con-' nected to the tubeby branch I01, the construction being such that'when the straight tube por- ,tion I05 is free or ice, the diaphragm will be expanded by its spring III, as shown, and when,

ice collects in the straight tube portion I05,' the diaphragm will becollapsed due to auction in the-pipe I01. The suction pump I99 may be I I2 designates. a

ductor connected to contact arm III, and I29 While the rotary contact'arm is in en-" gagement with the contact segment 95, a circuit is a conductor wire connected to the stationary contact III. As will be; understood, the modifled form of the ice detector and control tube illustrated in Fig. 3 may be substituted for the 5 venturi in the two forms of control illustrated in Figs. 1 and 2 of the drawings, the heating coil II2 of the straight tube portion I05, the contact arm H5 on the movable wall of the diaphragm, and the stationary contact H8 being 10 connected in the circuit similarly to the connections illustrated in Figs. 1 and 2.

In Fig. 4 is shown a cam make-and-break type in lieu of the rotary type switch shown in Fig. 2. It will be obvious that with suitable modification of design, this type switch may also be Figl. o This switch, as illustrated for substitution for the rotary switch 52 shown in Fig. 2, is shown 59 ton series of cams I22, I24, and I25, fixedly mounted on a shaft I25. The cams are provided I a respectively with recessed portions 94', 98, and 85', corresponding in relative design to the contactsegments'", 09, and 95 of switch 92; that is, the recess 24' in cam I22 is relatively a small.

3 are adapted to be commonly, electrically connected to the lead 92 from the manual selective switch 94. Each breaker is provided with a con-- ,tact adapted to engage a corresponding contact inan insulated mounting. panel I90. The breakers' are provided with electrically insulated lobes tact arm 91, inner ring contact 92,- conductor 92,

adapted. to'cooperate with the cams so that the contacts on the breakers close the electrical circuits by engaging the contacts of the panel I when the lobes'are in the cam recesses, and open the circuit when the lobes are out of the recesses To the contacts in the mounting panel are secured leads 95, 99, and 9I. It will thus be seen that lead 90 is adapted to provide a circult through breaker I21" which corresponds to the circuit through switch arm 91 and segment 94 ofiswitch 92; lead 99 is adapted to provide a circuit through'breaker I29 which corresponds to the circuit through-switchr arm 01 and segment 99 of switch 82; and lead 9| is adapted to provide a circuit through breaker I29 which corresponds to'the' circuitthrough switch arm 21 andsegment 55 of switch 02. The operation of the modification shown in Fig.2, when, used with this switch shown in Fig. 4, is such that when the circuit is closed at contacts 20 and II the circuit is completed to motor 1I throughhonductors" and 92 and lead 90, breaker I21 andlead' 92, since the lobe of breaker I21 is designed to rest in the recess 94 of cam 5 I22 in-the position of the switch during periods ..of inoperation of the anti-leer apparatus. The closing of the circuitat contacts and 5| starts the operation of the motor, causing the cams to rotate in a counterclockwise direction. The 70 circuit made by breaker I21 is then opened, and the lobe of breaker I20drops into the recess 95' of cam I24, closing the circuit to the heater 19 through lead 92, breaker I29, and lead 99. Continued rotation of .the'cam I24 again forces the 15 lobe of breaker I29 out of recess 95'. discontion of the corresponding partsin the construc-.

switch which 1s designed and illustrated for use used in lieu of the rot y ype switches shown in Sl-the motor 1| being set in operation to o L with motor 1I connected through reduction gear are a series of breakers I21, I28, and I29, which 9l, breaker 129, and lead 93.

In this manner the operation of the anti-icer apparatus will be controlled exactly as described in connection with vthe modification shown in Fig. 2.

Having thus described our invention, whatwe claim is:

1. In a power actuated de=icing apparatus,

' means for automatically controlling the operation of said apparatus, including an electric circuit, an electric motor, andmeans responsive to the formation of ice thereon adapted to close said circuit when ice collects on said last-mentioned means and to open the circuit when the ice is melted, electric heating means for said,

last-mentioned means, an electric circuit for the heating means, and a'switch in said last-mentioned circuit, said switch being operatively connected to said motor in such manner that it is adapted when actuated by the motor to close the circuit of the heating means for short intervals.

2. Means for automatically controlling the operation of apparatus for preventing the accumulation of ice on aircraft surfaces, said means including an electric circuit having a source of energy, a, motor in said circuit for operating saidapparatus, switch means in saidcircuit for connecting said motor with said source of energy, a second motor for operating said switch means, and a circuit for said second motor, comprising ice formation-responsive means adapted to close said last-mentioned circuit when ice forms on said ice formation responsive means and to open said circuit when ice formaresponsive to the formation of ice thereon adapt-' ed to close both of said motor circuits when ice collects on said means and toopen said circuits when the ice is melted, an electric heater for ed during a partial revolution thereof to open the circuit through the second motor to stop rotation of the switches and to close a circuitthrough the heater, the other switch during a partial revolution thereof acting to close acir cuit through the first-mentioned motor during the interval the second motor stops, and said last-mentioned means when the ice thereon is melted closing a, circuit through the second m0- tor to turn the switches to open the heater circuit ,and both of the motor circuits.

said last-mentioned means, an electric circuit for the heater, a rotary switch, and a reduction drive gear connection between the switch-and the second electric motor, said switch being adapted to intermittently open and close the circuit of said heater during operation of said apparatus.

4. The combination with apparatus for preventing the accumulation of ice on aircraft surfaces, of an electric circuit, an electric motor in the circuit for operating said apparatus, and means for automatically controlling the operation "of said apparatus, including a pair of rotary switches in the circuit, a second electric motor with circuit connections therefor for operating. said switches, reduction drive gear con- -5. The combination with apparatus for preventing the accumulation of ice on aircraft surfaces, of an electric circuit, an electric motor in the circuit for operating said apparatus, and means for automatically controlling the operation of said apparatus, including a pair of rotary switches in the circuit, a second electric motor with circuit connections therefor for operating said switches, a reduction drive gear cormection between each of the switches and the second motor for turning the switches in .unison, a tube for accelerated passage of air therethrough having oneend thereof facing towardthe front of the aircraft, a suctionfresponsive element opera tively connected with said tube and being responsive to change of pressure in the tube, said suction responsive element being adapted to close circuits through both of the motors when ice collects, in said tube, anelectric heater for said tube with circuit connections for the heater, one of said switches being adapted in the course of a partial revolution thereof to open the circuit through the second motor to stop rotation of the switches and to close a circuit through the heater, the other switch during a partial rotation thereof acting to close the circuitthrough the first-mentionedmotor during the interval the'second motor stops, and said suction responsive element when the ice in said tube ismelted closing a, circuit, through the second motor to turn the switches to open the heater circuitand both of the motor'circuits.

6. The combination with apparatus for preventing the accumulation of ice on a surface of an aircraft, said apparatus including power means for actuating same, of means responsive to ice formation for rendering said power means operative when ice forms thereon and inoperative when ice is removed therefrom, said last-mentioned means comprising a tube, a suction pump connected with said tuberearwardly of the forsurface, means responsive to ice formation. for

initiating operation of said apparatus comprise= ing an open tube having one end thereof facing toward the front of said vehicle and having inner contours to form a venturi such that a suction is created at the Venturi throat by the flow I of air through said tube, a suction-responsive element communicatively connected to said tube at the zone of suction, and means associated with said element for rendering said apparatus operativewhen ice is formed in said tube, stoppingthe suction, and for rendering said apparatus inoperative when said tube is free from ice and air is flowing therethrough.

8. In an automatic control device for controlsaid contact means comprising a Venturi tube positioned in the airstream forunobstructed flow therethrough, a conduit connected to the throat of said venturi such that flow through the latter normally produces a reduced pressure insaid conduit while icing of the walls of said venturi blocks off the communication with saidconduit, a, restricted vent connection betweensaid conduit and the atmosphere, and .a pressure responsive means operatively associated with said contacts and connected to said conduit and operative upon a predetermined reduction in pressure in said conduit to open said contacts to de-energize said electric circuit.

9. In an automatic control system for controlling-apparatus for de-icing aircraft surfaces, an electric circuit for rendering said apparatus operative and inoperative, switch contact means operative to control the energizing of said electric circuit, means normally biasing said contact means to open said electric circuit, and means responsive to ice formation for controlling operation of said contact means comprising a tube having an open end positioned in the airstream, a conduit connected to the other end of said tube,

- said tube when unobstructed by ice serving as a vent for said conduit to the atmospherasuction producing means tending .to continuously withdraw air from said conduit, and a pressure responsive device operatively associated with said contact means and connected to said conduit and operative upon a predetermined reduction in pressure within said conduit to close said contact means to energize said electric circuit.

GEORGE V. H OLLOMAN. WILLIAM E. HUFFMAN. 

